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package net
import (
var ErrLinkNotFound = errors.New("Link not found")
// NB: The following function is unsafe, because:
// - It changes a network namespace (netns) of an OS thread which runs
// the function. During execution, the Go runtime might clone a new OS thread
// for scheduling other go-routines, thus they might end up running in
// a "wrong" netns.
// - runtime.LockOSThread does not guarantee that a spawned go-routine on
// the locked thread will be run by it. Thus, the work function is
// not allowed to spawn any go-routine which is dependent on the given netns.
// Please see
// for more details and make sure that you understand the implications before
// using the function!
func WithNetNSUnsafe(ns netns.NsHandle, work func() error) error {
defer runtime.UnlockOSThread()
oldNs, err := netns.Get()
if err == nil {
defer oldNs.Close()
err = netns.Set(ns)
if err == nil {
defer netns.Set(oldNs)
err = work()
return err
func WithNetNSLinkUnsafe(ns netns.NsHandle, ifName string, work func(link netlink.Link) error) error {
return WithNetNSUnsafe(ns, func() error {
link, err := netlink.LinkByName(ifName)
if err != nil {
if err.Error() == errors.New("Link not found").Error() {
return ErrLinkNotFound
return err
return work(link)
var WeaveUtilCmd = "weaveutil"
// A safe version of WithNetNS* which creates a process executing
// "nsenter --net=<ns-path> weaveutil <cmd> [args]".
func WithNetNS(nsPath string, cmd string, args ...string) ([]byte, error) {
var stdout, stderr bytes.Buffer
args = append([]string{"--net=" + nsPath, WeaveUtilCmd, cmd}, args...)
c := exec.Command("nsenter", args...)
c.Stdout = &stdout
c.Stderr = &stderr
if err := c.Run(); err != nil {
return nil, fmt.Errorf("%s: %s", string(stderr.Bytes()), err)
return stdout.Bytes(), nil
func WithNetNSByPid(pid int, cmd string, args ...string) ([]byte, error) {
return WithNetNS(NSPathByPid(pid), cmd, args...)
func NSPathByPid(pid int) string {
return NSPathByPidWithRoot("/", pid)
func NSPathByPidWithRoot(root string, pid int) string {
return filepath.Join(root, fmt.Sprintf("/proc/%d/ns/net", pid))